var xmlHttp;
function check_userinfo(str)
{
	if (str.length==0){ 
		document.getElementById("user_info").innerHTML="* 不能为空！";
		return false;
	}
	xmlHttp=GetXmlHttpObject()
	if (xmlHttp==null){
		alert ("Browser does not support HTTP Request");
		return;
	} 
	var url="../ajax/show_info.php";
        alert("url");
	url=url+"?q="+str;
	url=url+"&sid="+Math.random();
	xmlHttp.onreadystatechange=stateChanged;
	xmlHttp.open("GET",url,true);
	xmlHttp.send(null);
}